Selectivity of the highly preorganized tetradentate ligand 2,9-di(pyrid-2-yl)-1,10-phenanthroline for metal ions in aqueous solution, including lanthanide(III) ions and the uranyl(VI) cation.

Some metal ion complexing properties of DPP (2,9-Di(pyrid-2-yl)-1,10-phenanthroline) are reported with a variety of Ln(III) (Lanthanide(III)) ions and alkali earth metal ions, as well as the uranyl(VI) cation. The intense π-π* transitions in the absorption spectra of aqueous solutions of 10(-5) M DPP were monitored as a function of pH and metal ion concentration to determine formation constants of the alkali-earth metal ions and Ln(III) (Ln = lanthanide) ions. It was found that log K(1)(DPP) for the Ln(III) ions has a peak at Ln(III) = Sm(III) in a plot of log K(1) versus 1/r(+) (r(+) = ionic radius for 8-coordination). For Ln(III) ions larger than Sm(III), there is a steady rise in log K(1) from La(III) to Sm(III), while for Ln(III) ions smaller than Sm(III), log K(1) decreases slightly to the smallest Ln(III) ion, Lu(III). This pattern of variation of log K(1) with varying size of Ln(III) ion was analyzed using MM (molecular mechanics) and DFT (density functional theory) calculations. Values of strain energy (∑U) were calculated for the [Ln(DPP)(H(2)O)(5)](3+) and [Ln(qpy)(H(2)O)(5)](3+) (qpy = quaterpyrdine) complexes of all the Ln(III) ions. The ideal M-N bond lengths used for the Ln(III) ions were the average of those found in the CSD (Cambridge Structural Database) for the complexes of each of the Ln(III) ions with polypyridyl ligands. Similarly, the ideal M-O bond lengths were those for complexes of the Ln(III) ions with coordinated aqua ligands in the CSD. The MM calculations suggested that in a plot of ∑U versus ideal M-N length, a minimum in ∑U occurred at Pm(III), adjacent in the series to Sm(III). The significance of this result is that (1) MM calculations suggest that a similar metal ion size preference will occur for all polypyridyl-type ligands, including those containing triazine groups, that are being developed as solvent extractants in the separation of Am(III) and Ln(III) ions in the treatment of nuclear waste, and (2) Am(III) is very close in M-N bond lengths to Pm(III), so that an important aspect of the selectivity of polypyridyl type ligands for Am(III) will depend on the above metal ion size-based selectivity. The selectivity patterns of DPP with the alkali-earth metal ions shows a similar preference for Ca(II), which has the most appropriate M-N lengths. The structures of DPP complexes of Zn(II) and Bi(III), as representative of a small and of a large metal ion respectively, are reported. [Zn(DPP)(2)](ClO(4))(2) (triclinic, P1, R = 0.0507) has a six-coordinate Zn(II), with each of the two DPP ligands having one noncoordinated pyridyl group appearing to be π-stacked on the central aromatic ring of the other DPP ligand. [Bi(DPP)(H(2)O)(2)(ClO(4))(2)](ClO(4)) (triclinic, P1, R = 0.0709) has an eight-coordinate Bi, with the coordination sphere composed of the four N donors of the DPP ligand, two coordinated water molecules, and the O donors of two unidentate perchlorates. As is usually the case with Bi(III), there is a gap in the coordination sphere that appears to be the position of a lone pair of electrons on the other side of the Bi from the DPP ligand. The Bi-L bonds become relatively longer as one moves from the side of the Bi containg the DPP to the side where the lone pair is thought to be situated. A DFT analysis of [Ln(tpy)(H(2)O)(n)](3+) and [Ln(DPP)(H(2)O)(5)](3+) complexes is reported. The structures predicted by DFT are shown to match very well with the literature crystal structures for the [Ln(tpy)(H(2)O)(n)](3+) with Ln = La and n = 6, and Ln = Lu with n = 5. This then gives one confidence that the structures for the DPP complexes generated by DFT are accurate. The structures generated by DFT for the [Ln(DPP)(H(2)O)(5)](3+) complexes are shown to agree very well with those generated by MM, giving one confidence in the accuracy of the latter. An analysis of the DFT and MM structures shows the decreasing O--O nonbonded distances as one progresses from La to Lu, with these distances being much less than the sum of the van der Waals radii for the smaller Ln(III) ions. The effect that such short O--O nonbonded distances has on thermodynamic complex stability and coordination number is then discussed.

Synthesis of new bergenin derivatives as potent inhibitors of inflammatory mediators NO and TNF-α.

Bergenin is an isocoumarin natural product which aides in fat loss, healthy weight maintenance, enhancing the lipolytic effects of norepinephrine, inhibiting the formation of interleukin 1α and cyclooxygenases-2. Here we describe the anti-inflammatory activity of new bergenin derivatives 1-15 in the respiratory burst assay. Bergenin was isolated from the crude extract of Mallotus philippenensis after repeated column chromatography and was then subjected to chemical derivatization. The structures of all compounds were elucidated by NMR and mass spectroscopic techniques. Compound 2 was also studied using single crystal X-ray diffraction. Compounds 4, (54.5±2.2%) 5 (47.5±0.5%) 5, and 15 (86.8±1.9%) showed significant (P≤0.005) NO inhibitory activities whereas 6, 7, 11, 12 and 13 displayed moderate inhibitory activities that ranges between 16% and 31%. Furthermore compounds 4 and 15, were discovered as significant (P≤0.005) TNF-α inhibitors with 98% and 96% inhibition, respectively, while compounds 3, 5, 7, 8, 11, and 12 showed low level of TNF-α inhibition (0.4-28%). Compounds 8, 13 and 15 exhibited moderate anti-inflammatory IC(50) activities with 212, 222, and 253 µM, respectively, compared to the standard anti-inflammatory drug indomethacin as well as the parent bergenin compound. No cytotoxic effects could be detected when the compounds were tested on 3T3 cells up to concentrations of 100 µM.

Metal-ion-complexing properties of 2-(pyrid-2'-yl)-1,10-phenanthroline, a more preorganized analogue of terpyridyl. A crystallographic, fluorescence, and thermodynamic study.

Some metal-ion-complexing properties of the ligand 2-(pyrid-2'-yl)-1,10-phenanthroline (MPP) are reported. MPP is of interest in that it is a more preorganized version of 2,2';6,2''-terpyridine (tpy). Protonation constants (pK(1) = 4.60; pK(2) = 3.35) for MPP were determined by monitoring the intense π-π* transitions of 2 × 10(-5) M solutions of the ligand as a function of the pH at an ionic strength of 0 and 25 °C. Formation constants (log K(1)) at an ionic strength of 0 and 25 °C were obtained by monitoring the π-π* transitions of MPP titrated with solutions of the metal ion, or 1:1 solutions of MPP and the metal ion were titrated with acid. Large metal ions such as Ca(II) or La(III) showed increases of log K(1) of about 1.5 log units compared to that of tpy. Small metal ions such as Zn(II) and Ni(II) showed little increase in log K(1) for MPP compared to the tpy complexes, which is attributed to the presence of five-membered chelate rings in the MPP complexes, which favor large metal ions. The structure of [Cd(MPP)(H(2)O)(NO(3))(2)] (1) is reported: monoclinic, P2(1)/c, a = 7.4940(13) Å, b = 12.165(2) Å, c = 20.557(4) Å, ß = 96.271(7)°, V = 1864.67(9) Å(3), Z = 4, and final R = 0.0786. The Cd in 1 is seven-coordinate, comprising the three donor atoms of MPP, a coordinated water, a monodentate, and a bidentate NO(3)(-). Cd(II) is a fairly large metal ion, with r(+) = 0.96 Å, slightly too small for coordination with MPP. The effect of this size matching in terms of the structure is discussed. Fluorescence spectra of 2 × 10(-7) M MPP in aqueous solution are reported. The nonprotonated MPP ligand fluoresces only weakly, which is attributed to a photoinduced-electron-transfer effect. The chelation-enhanced-fluorescence (CHEF) effect induced by some metal ions is presented, and the trend of the CHEF effect, which is Ca(II) > Zn(II) > Cd(II) ~ La(III) > Hg(II), is discussed in terms of factors that control the CHEF effect, such as the heavy-atom effect.

Synthesis of cis and trans bis-alkynyl complexes of Cr(III) and Rh(III) supported by a tetradentate macrocyclic amine: a spectroscopic investigation of the M(III)-alkynyl interaction.

Alkynyl complexes of the type [M(cyclam)(CCR)(2)]OTf (where cyclam = 1,4,8,11-tetraazacyclotetradecane; M = Rh(III) or Cr(III); and R = phenyl, 4-methylphenyl, 4-trifluoromethylphenyl, 4-fluorophenyl, 1-naphthalenyl, 9-phenanthrenyl, and cyclohexyl) were prepared in 49% to 93% yield using a one-pot synthesis involving the addition of 2 equiv of RCCH and 4 equiv of BuLi to the appropriate [M(cyclam)(OTf)(2)]OTf complex in THF. The cis and trans isomers of the alkynyl complexes were separated using solubility differences, and the stereochemistry was characterized using infrared spectroscopy of the CH(2) rocking and NH bending region. All of the trans-[M(cyclam)(CCR)(2)]OTf complexes exhibit strong Raman bands between 2071 and 2109 cm(-1), ascribed to ν(s)(C≡C). The stretching frequencies for the Cr(III) complexes are 21-28 cm(-1) lower than for the analogous Rh(III) complexes, a result that can be interpreted in terms of the alkynyl ligands acting as π-donors. UV-vis spectra of the Cr(III) and Rh(III) complexes are dominated by strong charge transfer (CT) transitions. In the case of the Rh(III) complexes, these CT transitions obscure the metal centered (MC) transitions, but in the case of the Cr(III) complexes the MC transitions are unobscured and appear between 320 and 500 nm, with extinction coefficients (170-700 L mol(-1) cm(-1)) indicative of intensity stealing from the proximal CT bands. The Cr(III) complexes show long-lived (240-327 µs), structureless, MC emission centered between 731 and 748 nm in degassed room temperature aqueous solution. Emission characteristics are also consistent with the arylalkynyl ligands acting as π-donors. The Rh(III) complexes also display long-lived (4-21 µs), structureless, metal centered emission centered between 524 and 548 nm in degassed room temperature solution (CH(3)CN).

Optical imaging in tissue with X-ray excited luminescent sensors.

We report a high-spatial resolution imaging technique to measure optical absorption and detect chemical and physical changes on surfaces embedded in thick tissue. Developing sensors to measure chemical concentrations on implanted surfaces through tissue is an important challenge for analytical chemistry and biomedical imaging. Tissue scattering dramatically reduces the resolution of optical imaging. In contrast, X-rays provide high spatial resolution imaging through tissue but do not measure chemical concentrations. We describe a hybrid technique which uses a scanning X-ray beam to irradiate Gd(2)O(2)S scintillators and detect the resulting visible luminescence through the tissue. The amount of light collected is modulated by optical absorption in close proximity to the luminescence source. By scanning the X-ray beam, and measuring total amount of light collected, one can measure the local absorption near scintillators at a resolution limited by the width of luminescence source (i.e. the width of the X-ray excitation beam). For proof of principle, a rectangular 1.7 mm scanning X-ray beam was used to excite a single layer of 8 µm Gd(2)O(2)S particles, and detect the absorption of 5 nm thick silver island film through 10 mm of pork. Lifetime and spectroscopic measurements, as well changing the refractive index of the surroundings indicate that the silver reduces the optical signal through attenuated total internal reflection. The technique was used to image the dissolution of regions of the silver island film which were exposed to 1 mM of H(2)O(2) through 1 cm of pork tissue.

High-resolution chemical imaging through tissue with an X-ray scintillator sensor.

We describe a novel method for high-resolution chemical imaging on a surface embedded in tissue. The sensor surface consists of an X-ray scintillator film coated in a thin film loaded with chemical indicator dye. A narrow scanning X-ray beam is used to excite luminescence from X-ray scintillators located within the beam. This luminescence passes through the indicator film, and the spectrum is analyzed to measure chemical concentrations at that location. A pH sensor is demonstrated with a dynamic range between pH 6-9 and noise level of 0.05 pH units using methyl-red dyed pH paper. The location of the interface between two types of scintillator films is obtained with 0.30 mm spatial resolution even though the images are highly blurred by 10 mm of chicken breast. This work has important applications for detecting pH changes on surfaces of implanted medical devices.

6,7-Dihydro-3H-1,4-diazepino[1,2,3,4-lmn][1,10]phenanthroline-3,9(5H)-dione.

In the title compound, C(15)H(12)N(2)O(2), the seven-membered ring bearing the three methyl-ene C atoms displays a puckered conformation, with the methyl-ene C atoms deviating from the plane of the benzene ring by 0.05 (1), 0.98 (1) and 1.04 (1) Å. The phenanthroline unit is not planar; the dihedral angles between this benzene ring and the other pyridyl rings are 9.62 (4) and 9.31 (4)°. The crystal packing is stabilized by π-π inter-actions between two phenanthroline ring systems, forming a centrosymmetric dimer with a centroid-centroid distance of 3.656 (1) Å.

Diethyl 2,2'-(biphenyl-2,2'-diyldi-oxy)diacetate.

In the title compound, C(20)H(22)O(6), the mean planes through the benzene rings make a dihedral angle of 59.82 (7)° with each other. Weak inter-molecular C-H⋯O inter-actions together with π-π stacking inter-actions [centroid-centroid distance = 3.830 (1) Å] between benzene rings are observed in the crystal packing.

Thiacrown Pt(II) complexes with group 15 donor ligands: pentacoordination in Pt(II) complexes.

We report the synthesis and full characterization for a series of thiacrown complexes of Pt(II) incorporating the fluxional trithiacrown ligand 1,4,7-trithiacyclononane ([9]aneS3) and several group 15 donors ligands. Reaction of [Pt([9]aneS3)Cl2] with a full stoichiometric equivalent of the group 15 donor (L = 2 x AsPh3, SbPh3 or 1,2-bis(diphenylarsenio) ethane (dpae) followed by metathesis with NH4PF6 yields [Pt([9]aneS3)L](PF6)2. We also report the analogous Pd(II) complex with dpae. Similar reactions of the starting Pt complex with one equivalent of XPh3 (X = As or Sb) result in complexes of the formula [Pt([9]aneS3)(XPh3)(Cl)](PF6). All six new complexes have been fully characterized by multinuclear NMR, IR, and UV-Vis spectroscopies in addition to elemental analysis and single crystal structural determinations. The X-ray structures of each complex indicate an axial M-S interaction formed by the endodentate conformation of the [9]aneS3 ligand. The axial M-S distance is highly dependent upon the ancillary donor set. The axial M-S distance shortens with the identity of the group 15 donor ligand according to the trend, Sb < As < P, due to their increasingly poorer donor qualities. The two bis pnictogen complexes, [Pt([9]aneS3)(AsPh3)2](PF6)2 and [Pt([9]aneS3)(SbPh3)2](PF6)2 form unusual five-coordinate distorted trigonal bipyramids in contrast to the pseudo-five coordinate, elongated square pyramidal structures typically observed in Pt(II) complexes of [9]aneS3. The distortion arises from intramolecular pi-pi interactions between the phenyl rings on the two different triphenyl ligands. Chemical shifts in the 195Pt NMR also show similar periodic relationships which trend progressively upfield as the donor atom becomes larger. As expected, the coordinated [9]aneS3 ligand shows fluxional behavior in its NMR spectra, resulting in a single 13C NMR resonance, despite the asymmetric coordination environment found in both chloro complexes. The line width for the carbon NMR resonance as well as for the 195Pt NMR peak is highly sensitive to the nature of the group 15 donor, with poorer donors such as SbPh3 showing significant line broadening. Measurements from the electronic spectra support that the ligand field strength of the pnictogen donor decreases with its increasing size.

Trigonal structures of ABe2BO3F2 (A = Rb, Cs, Tl) crystals.

Several interesting fluoroberyllium borates were synthesized hydrothermally and characterized by single-crystal X-ray diffraction. The crystal structures of RbBe(2)BO(3)F(2) (RBBF; rubidium fluoroberyllium borate) and CsBe(2)BO(3)F(2) (CBBF; caesium fluoroberyllium borate), previously determined in the space group C2, were reinvestigated for higher symmetry and found to have more suitable solutions in the space group R32. TlBe(2)BO(3)F(2) (TBBF; thallium fluoroberyllium borate) was synthesized as a novel compound also having this trigonal structure type. Details of the space-group determination and unique structural features are discussed. These crystal structures were compared with that of KBe(2)BO(3)F(2), revealing interesting structural trends within this family of compounds that are also discussed. A crystallographic explanation of the physical morphology is postulated.

Strong metal ion size based selectivity of the highly preorganized ligand PDA (1,10-phenanthroline-2,9-dicarboxylic acid) with trivalent metal ions. A crystallographic, fluorometric, and thermodynamic study.

The selectivity of the rigid ligand PDA (1,10-phenanthroline-2,9-dicarboxylic acid) for some M(III) (M = metal) ions is presented. The structure of [Fe(PDA(H)(1/2))(H(2)O)(3)] (ClO(4))(2).3H(2)O.(1)/(2)H(5)O(2) (1) is reported: triclinic, P1, a = 7.9022(16) A, b = 12.389(3) A, c = 13.031(3) A, alpha = 82.55(3) degrees , beta = 88.41(3) degrees , gamma = 78.27(3) degrees , V = 1238.6(4) A(3), Z = 2, R = 0.0489. The coordination geometry around the Fe(III) is close to a regular pentagonal bipyramid, with Fe-N lengths averaging 2.20 A, which is normal for a 1,10-phenanthroline type of ligand coordinated to seven-coordinate Fe(III). The Fe-O bonds to the carboxylate oxygens average 2.157 A, which is rather long compared to the average Fe-O length of 2.035 A to carboxylates in seven-coordinate Fe(III) complexes. The structure of 1 supports the idea that the Fe(III) is too small for ideal coordination in the cleft of PDA, and the structure shows that the Fe(III) adapts to this by inducing numerous small distortions in the structure of the PDA ligand. The log K(1) values for PDA at 25 degrees C in 0.1 M NaClO(4) were determined by UV spectroscopy with Al(III) (log K(1) = 6.9), Ga(III) (log K(1) = 9.7), In(III) (log K(1) = 19.7), Fe(III) (log K(1) = 20.0), and Bi(III) (log K(1) = 26.2). The low values of log K(1) for PDA with Al(III) and Ga(III) are because these ions are too small for the cleft in PDA, which requires a large metal ion with an ionic radius (r(+)) of 1.0 A. In(III) and Fe(III) (r(+) = 0.86 and 0.72 A for a coordination number (CN) of 7) are somewhat too small for the cleft in PDA but may adapt by increasing the coordination number, which increases the metal ion size, and have high log K(1) values. Very large log K(1) values are found, as expected, for Bi(III) (r(+) = 1.17 A, CN = 8), which fits the cleft quite well. Fluorescence studies show that Y(III) produces the largest CHEF (chelation enhanced fluorescence) effects, followed by La(III) and Lu(III), in the PDA complexes. Metal ions with nonfilled d or f subshells produce very large quenching of the fluorescence, as do heavy-metal ions such as In(III) and Bi(III), which have large spin-orbit coupling effects. The Al(III)/PDA complex produced an intense broad band at longer wavelength than the pi*-pi emissions of the PDA ligand, which is at a maximum at pH 6, and the possibility that this might reflect an exciplex, where one PDA ligand in the Al(III) complex pi-stacks with the excited state of a second PDA ligand, is discussed.

N,N'-Bis(4-methoxy-benzyl-idene)-4,4'-(m-phenyl-enedi-oxy)dianiline.

Mol-ecules of the title compound, C(34)H(28)N(2)O(4), a Schiff base precursor for macrocycles, are located on a mirror plane. The C=N double bond is trans configured. Inter-molecular C-H⋯O inter-actions stabilize the crystal packing.

Emissive chromium(III) complexes with substituted arylethynyl ligands.

Arylethynylchromium(III) complexes of the form trans-[Cr(cyclam)(CCC(6)H(4)R)(2)]OTf (where cyclam = 1,4,8,11-tetraazacyclotetradecane, R = H, CH(3), or CF(3) in the para position, and OTf = trifluoromethanesulfonate) have been prepared and characterized by IR spectroscopy and X-ray diffraction. The complexes are emissive with excited-state lifetimes in a deoxygenated fluid solution between 200 and 300 micros.

Cyclometallated Pt(II) and Pd(II) complexes with a trithiacrown ligand.

We report the synthesis and full characterization for a series of cyclometallated complexes of Pt(II) and Pd(II) incorporating the fluxional trithiacrown ligand 1,4,7-trithiacyclononane ([9]aneS3). Reaction of [M(C insertion mark N)(micro-Cl)]2 (M = Pt(II), Pd(II); C insertion mark N = 2-phenylpyridinate (ppy) or 7,8-benzoquinolinate (bzq)) with [9]aneS3 followed by metathesis with NH4PF6 yields [M(C insertion mark N)([9]aneS3)](PF6). The complexes [M(C insertion mark P)([9]aneS3)](PF6) (M = Pt(II), Pd(II); Cinsertion markP = [CH2C6H4P(o-tolyl)2-C,P]-) were synthesized from their respective [Pt(C insertion mark P)(micro-Cl)]2 or [Pd(C insertion mark P)(micro-O2CCH3)]2 (C insertion mark P) starting materials. All five new complexes have been fully characterized by multinuclear NMR, IR and UV-Vis spectroscopies in addition to elemental analysis, cyclic voltammetry, and single-crystal structural determinations. As expected, the coordinated [9]aneS3 ligand shows fluxional behavior in its NMR spectra, resulting in a single 13C NMR resonance despite the asymmetric coordination environment of the cyclometallating ligand. Electrochemical studies reveal irreversible one-electron metal-centered oxidations for all Pt(II) complexes, but unusual two-electron reversible oxidations for the Pd(II) complexes of ppy and bzq. The X-ray crystal structures of each complex indicate an axial M-S interaction formed by the endodentate conformation of the [9]aneS3 ligand. The structure of [Pd(bzq)([9]aneS3)](PF6) exhibits disorder in the [9]aneS3 conformation indicating a rare exodentate conformation as the major contributor in the solid-state structure. DFT calculations on [Pt([9]aneS3)(ppy)](PF6) and [Pd([9]aneS3)(ppy)](PF6) indicate the HOMO for both complexes is primarily dz2 in character with a significant contribution from the phenyl ring of the ppy ligand and p orbital of the axial sulfur donor. In contrast, the calculated LUMO is primarily ppy pi* in character for [Pt([9]aneS3)(ppy)](PF6), but dx2-y2 in character for [Pd([9]aneS3)(ppy)](PF6).

Enhanced metal ion selectivity of 2,9-di-(pyrid-2-yl)-1,10-phenanthroline and its use as a fluorescent sensor for cadmium(II).

The metal ion complexing properties of the ligand DPP (2,9-di-(pyrid-2-yl)-1,10-phenanthroline) were studied by crystallography, fluorimetry, and UV-visible spectroscopy. Because DPP forms five-membered chelate rings, it will favor complexation with metal ions of an ionic radius close to 1.0 A. Metal ion complexation and accompanying selectivity of DPP is enhanced by the rigidity of the aromatic backbone of the ligand. Cd2+, with an ionic radius of 0.96 A, exhibits a strong CHEF (chelation enhanced fluorescence) effect with 10(-8) M DPP, and Cd2+ concentrations down to 10(-9) M can be detected. Other metal ions that cause a significant CHEF effect with DPP are Ca2+ (10(-3) M) and Na+ (1.0 M), whereas metal ions such as Zn2+, Pb2+, and Hg2+ cause no CHEF effect with DPP. The lack of a CHEF effect for Zn2+ relates to the inability of this small ion to contact all four donor atoms of DPP. The structures of [Cd(DPP)2](ClO4)2 (1), [Pb(DPP)(ClO4)2H2O] (2), and [Hg(DPP)(ClO4)2] (3) are reported. The Cd(II) in 1 is 8-coordinate with the Cd-N bonds to the outer pyridyl groups stretched by steric clashes between the o-hydrogens on these outer pyridyl groups and the central aromatic ring of the second DPP ligand. The 8-coordinate Pb(II) in 2 has two short Pb-N bonds to the two central nitrogens of DPP, with longer bonds to the outer N-donors. The coordination sphere around the Pb(II) is completed by a coordinated water molecule, and two coordinated ClO4(-) ions, with long Pb-O bonds to ClO4(-) oxygens, typical of a sterically active lone pair on Pb(II). The Hg(II) in 3 shows an 8-coordinate structure with the Hg(II) forming short Hg-N bonds to the outer pyridyl groups of DPP, whereas the other Hg-N and Hg-O bonds are rather long. The structures are discussed in terms of the fit of large metal ions to DPP with minimal steric strain. The UV-visible studies of the equilibria involving DPP and metal ions gave formation constants that show that DPP has a higher affinity for metal ions with an ionic radius close to 1.0 A, particularly Cd(II), Gd(III), and Bi(III), and low affinity for small metal ions such as Ni(II) and Zn(II). The complexes of several metal ions, such as Cd(II), Gd(III), and Pb(II), showed an equilibrium involving deprotonation of the complex at remarkably low pH values, which was attributed to deprotonation of coordinated water molecules according to: [M(DPP)(H2O)]n+ <==> [M(DPP)(OH)](n-1)+ + H+. The tendency to deprotonation of these DPP complexes at low pH is discussed in terms of the large hydrophobic surface of the coordinated DPP ligand destabilizing the hydration of coordinated water molecules and the build-up of charge on the metal ion in its DPP complex because of the inability of the coordinated DPP ligand to hydrogen bond with the solvent.

4,4'-Diiodo-3,3'-dimethoxy-biphen-yl.

The mol-ecules of the title compound, C(14)H(12)I(2)O(2), lie on inversion centers and are linked by I⋯O inter-actions with inter-molecular distances of 3.324 (3) Å. The aromatic rings display no significant inter-calation or stacking inter-actions.

2,2'-(Biphenyl-2,2'-diyldi-oxy)diaceto-hydrazide.

In the mol-ecule of the title compound, C(16)H(18)N(4)O(4), the dihedral angle between the mean planes of the two benzene rings is 56.76 (5)°. The crystal structure reveals extensive inter-molecular hydrogen bonds between carbonyl O atoms and primary amines, as well as between primary and secondary amines of hydrazide, forming rings of R(2) (2)(10) and R(2) (2)(6) motifs, respectively. The structure is further stabilized by intra-molecular and non-classical hydrogen bonds of the types N-H⋯O and C-H⋯O, respectively. The structure does not show any π-π inter-actions.

4-Iodo-3,3'-dimethoxy-biphen-yl.

Mol-ecules of the title compound, C(14)H(13)IO(2), exhibit no π-π inter-actions. The dihedral angle between the two aromatic rings is 43.72 (9)°. The shortest inter-molecular I⋯O distance is 3.408 (2) Å, which is significantly less than the sum of the van der Waals radii for I and O (3.50 Å).

Di-tert-butyl 2,2'-(biphenyl-2,2'-diyl-dioxy)diacetate.

The title compound, C(24)H(30)O(6), does not exhibit π-π inter-actions due to the steric effect of the bulky tert-butyl groups present in the mol-ecule. The presence of these groups at the 2 and 2' positions hinders the free motion of the benzene rings relative to each other, causing them to adopt an anti-periplanar arrangement. The benzene rings are twisted by just under 50.96 (17)° with respect to each other. The carbonyl groups within the mol-ecule are directed in different directions, one towards the biphenyl group and the other away from it. The mol-ecules are linked together by C=O⋯H-C hydrogen bonds.